UK is a horrible heroic. First boss is harder than a lot of the other heroics, and its a really crappy emblem/hr amount.

Second best is probably Culling of Strat if you take it slow and easy - 4 badges and you can practice your speed runs when you get confident. Drak'Tharon keep is also great - you'll probably need to skip the second boss at first (but you never know) - once you get it down its 4 badges in 20-25 minutes.